Born in Sturgeon Falls, Ontario, Blais attended Ecole Sacré-Coeur and Sturgeon Falls High School before receiving a Bachelor of Arts degree in 1961 and a Bachelor of Laws degree in 1964 from the University of Ottawa. He was called to the Ontario Bar in 1966 and created a Queen's Counsel in 1979. In 2001, he obtained a master's degree in International Law from the University of Ottawa.

Blais subsequently returned to practicing law. In 1994, he was appointed chair of the Pearson Peacekeeping Centre, holding that position until he retired in 2002. He was the Chairman of the Board of Directors of the University of Ottawa Heart Institute until 2012.

In August 2012, with the help of lawyer Mark Power, he contested the nomination of Auditor General Michael Ferguson, named in November 2011, on the grounds that, as a unilingual Anglophone, his nomination was illegal and unconstitutional. The court action refers to article 16 of the Canadian Charter of Rights and Freedoms and the Official Languages Act.